Cable shock absorbing device

ABSTRACT

A shock absorbing device for an electrical cable includes a resilient member attachable to two spaced-apart portions of the cable, so as to bias the spaced-apart portions toward one another and to impart an arcuate shape to the cable between the spaced apart portions. The device also includes a spacer member for location between the cable and the resilient member. The spacer member can ensure that the cable and the resilient member are maintained at a minimum distance, so that when tension is applied to the cable, the resilient member is deformed, thus producing a rising spring rate effect in the device.

The invention relates to a cable shock absorbing device for electriccables. Particularly, but not exclusively, the invention relates to acable shock absorbing device for use in connection with electricaldomestic appliances such as vacuum cleaners, hairdryers, other hair careappliances, power tools and other appliances which are manoeuvred duringnormal use.

Vacuum cleaners and other domestic or household electrical appliancesincorporate electrical cables which remain connected to a mains socketwhilst the device is manoeuvred during its normal use. The normalmovement of a domestic vacuum cleaner includes reciprocal action acrossa floor to be cleaned and, in some cases, this movement can result insharp increases in tension applied to the electric cable. Repeatedjerkings of the electric cable contribute to the vulnerability of thecable to failure and are therefore preferably avoided. Unfortunately,normal domestic use of such machines can be reasonably vigorous and fullelimination of sudden jerking movements of the electric cable of avacuum cleaner or a similar device is impossible to achieve.

Some attempt has been made to introduce shock absorbing capabilities tocables to which sudden high loading is occasionally applied. An exampleof this is described in U.S. Pat. No. 4,992,629 which relates toapparatus for absorbing cable shock in underground cables. Thedisclosure details a three part housing inside which the cable is loopedwhen it is not under tension. When the cable is placed under tension,the housing expands against the action of a return spring so as to allowthe looped portion of the cable to extend. The damping action of thespring ensures that the increase in tension applied to the cable isabsorbed. This type of arrangement is unsuitable for use in relation tothe electric cable of a domestic appliance because of its complexity,cost and bulk. Furthermore, such a device would be difficult to fitretroactively to an existing appliance in order to extend the life ofthe cable.

It is an object of the present invention to provide a cable shockabsorbing device suitable for use with domestic electrical appliances,particularly vacuum cleaners. It is a further object of the presentinvention to provide a cable shock absorbing device which is simple andeasy to manufacture at low cost. It is a further object of the inventionto provide a cable shock absorbing device which is compact and whichdoes not compromise volume when the cable is stored. It is a furtherobject of the invention to provide a shock absorbing device for anelectric cable which can be quickly and easily fitted to the electriccable of an existing domestic appliance such as a vacuum cleaner.

The invention provides a shock absorbing device for an electric cablecomprising a resilient member attachable to two spaced-apart portions ofthe cable so as to bias the said portions towards one another and toimpart an arcuate shape to the cable between the said portions, thedevice further comprising a spacer member for location between the cableand the resilient member. Further and advantageous features are set outin the subsidiary claims.

The device of the invention is simple and easy to manufacture, therebyproviding a low-cost solution to the problem of vigorous jerkingmovements being applied to electrical cables. The provision of theresilient member between two spaced-apart portions of the cable allowsany jerking movement to be damped so that the risk of the life of thecable being reduced is itself reduced. The provision of the spacermember between the cable and the resilient member ensures that a minimumdistance is maintained between the cable and the resilient member which,in some embodiments, means that the resilient member will be deformed bythe spacer member as tensile stress is applied to the cable. Thisdistortion of the resilient member increases the tensile stress withinthe resilient member and thus increases the resistance of the device tothe “straightening” of the cable under axial forces. The effect is toprovide a rising spring rate which is highly advantageous in preventingsudden jerking movements being applied to the cable of a domesticelectrical appliance.

Further and more particular advantages of the arrangement of theinvention will become clear during the following description ofpreferred embodiments of the invention which are given by way of exampleonly.

In the drawings:

FIG. 1a is a front view of a spacer member forming part of a shockabsorbing device according to the invention;

FIG. 1b is a side view of the spacer member of FIG. 1a;

FIG. 1c is a section through the spacer member of FIG. 1a taken alongthe line I—I;

FIG. 2 is a perspective view of a resilient member forming part of ashock absorbing device according to the invention;

FIGS. 3a to 3 e illustrate a method by which the shock absorbing deviceof FIGS. 1 and 2 can be fitted to the cable of an electrical appliance;

FIG. 4a illustrates the device of FIGS. 1 to 3 in use in a relaxedstate;

FIG. 4b illustrates the device of FIGS. 1 to 3 in use in a functioningstate;

FIG. 5 is a graph showing the results of testing carried out in respectof the resilient member forming part of the shock absorbing device shownin FIGS. 1 to 4;

FIGS. 6 to 8 show, in side view, alternative embodiments of a deviceaccording to the invention having resiliently deformable spacer members;

FIG. 9 illustrates further embodiments of the invention in which theresilient member is formed integrally with or fixedly attached to thespacer member;

FIGS. 10 to 12 illustrate further embodiments of the invention in whichthe resilient member is retained at a fixed distance from the cable bydifferent means; and

FIG. 13 illustrates an embodiment of the invention incorporating bracingarms designed to guide the cable into a linear shape outside theconfines of the device.

The components of a shock absorbing device according to the inventionare illustrated in FIGS. 1 and 2. Essentially, the device consists of aspacer member 10 as shown in FIG. 1, and a resilient member 20 as shownin FIG. 2. The spacer member 10 is generally annular in shape and hastwo opposing faces 12, 14, each of which is planar. The planes of theopposing faces 12, 14 are inclined to one another at an angle ofapproximately 15°. Around the periphery of the spacer member 10 andlying between the opposing faces 12, 14 is an annular groove 16. In thearea in which the faces 12, 14 are closest together, the groove 16 has apart-circular cross section as illustrated in FIGS. 1b and 1 c. Thegroove 16 changes shape in the area in which the faces 12, 14 arefurthest apart and adopts a triangular profile for reasons which will beexplained below.

The spacer member 10 has retaining means 18 in the form of two opposinghook members located in the area in which the opposing faces 12, 14 arefurthest apart. The hook members 18 extend generally inwardly of thespacer member 10 towards one another and comprise upwardly extendinghook portions 18 a. The hook portions 18 a extend generally parallel tothe triangular surface of the groove 16 and, together with thetriangular surface of the groove 16, delimit two opposing channels 18 b.The purpose of the opposing channels will be described and explainedbelow.

In the embodiment illustrated, the outer diameter of the spacer memberis approximately 27 mm and the diameter of the central aperture isapproximately 14 mm. The groove 16 has a diameter of approximately 6 mmand the width of the opposing channels 18 b is approximately 2 mm. Thespacer member 10 is manufactured by moulding from a plastics materialsuch as polyethylene. The hook members 18 are formed integrally with themember 10 during manufacture. The simplicity of the shape of the spacermember 10 makes it easy and cheap to produce. The function of theannular shape, apart from the aesthetic aspects, is to reduce the weightof the spacer member 10 as far as possible and to provide for easyhandling and manipulation. It will be appreciated that the diameter ofthe groove 16 can be varied to accomnodate different sizes of cable and,ideally, the groove is dimensioned to match the cable diameter.

The resilient member 20 illustrated in FIG. 2 is an essential componentof the shock absorbing device of the invention. The resilient member 20is formed by a simple band made from synthetic rubber and possessing theresilient characteristics necessary to resist repeated deformation overa significant period of time. The material must also be capable ofresisting deterioration due to environmental factors such as the effectsof ozone and UV light. Ideally, the band 20 has a rectangular crosssection with the depth of the band being between 2 and 4 times thethickness thereof. In the preferred embodiment, the depth of the band issubstantially 7 mm and the thickness is substantially 2.3 mm. If theband were to be formed into a circular shape in the relaxed state, itwould have a diameter of approximately 17 mm. The band 20 can be formedby any known method.

The preferred method of applying the device described above to a cablein order to provide the cable with a shock absorbing capability and thusreduce the vulnerability of the cable to failure due to repeated jerkingmovements will now be described with reference to FIG. 3. Initially, asshown in FIG. 3a, the cable 30 is formed into a loose U shape and thecable is passed through the resilient band 20 as shown in FIG. 3b sothat the arms 32 of the U shape are held together by the resilient band20. At this stage, the size of the U shape is significantly greater thanthe dimensions of the spacer member 10. The spacer member 10 is thenintroduced to the interior of the U shaped part of the cable between thebase 34 of the U shape and the resilient band 20 as shown in FIG. 3c.The size of the U shape allows the spacer member 10 to be easilyinserted into this space. The arms 32 of the U shape of the cable arethen pulled apart so as to force the resilient member 20 closer to thebase 34 of the U shape until it comes into contact with the spacermember 10. The fact that the opposing faces 12, 14 of the spacer member10 are relatively widely spaced apart in this area, together with thefact that the resilient member is under tension at this stage, meansthat the resilient member 20 will tend to pass into the groove 16 ratherthan over the outer surfaces of the faces 12, 14. The inclined hookportions 18 a will also encourage the resilient member to pass into theinterior of the groove 16.

Continued and increased application of tension to the arms 32 of the Ushape of the cable will then force the resilient member 20 further intothe groove 16. The geometry of the device will then encourage theresilient band 20 to become lodged in the opposing channels 18 b asshown in FIG. 3e. Because the lodging of the resilient member 20 in thechannels 18 b takes place when the band 20 is under a substantial amountof tension, the thickness of the band 20 at the appropriate time isreduced compared to its normal thickness. The band 20 is thus able toenter the channels 18 b, despite the fact that the depth of the channelsis less than the thickness of the band when in its relaxed state.However, when the cable is released and the device is allowed to take upits relaxed state position, the thickness of the resilient band returnsto normal and the band 20 becomes gripped by the hook portions 18. Theband 20 is thus held fixedly on the spacer member 10 during normal use.This has the advantage that, should the resilient band 20 break, theband will be held securely on the spacer member by one or other of thehook portions 18 and the risk of injury to a user or other person willbe greatly reduced in comparison to the risk if the band 20 were not soheld. Once the resilient member 20 has been brought into the positionshown in FIG. 3e, the tension in the cable 30 can be released. Theresilient band 20 will remain in contact with the cable 30 at the pointsto which it was forced to move during the installation process but willbe held at. these points merely by friction between the cable 30 and theband 20. If the cable to which the device is to be applied is coated orsheathed with a material which is not conducive to the maintenance ofthe resilient member 20 at the appropriate points, then the resilientmember may need to be coated with a suitable slip-resistant material orelse the resilient band 20 can be affixed to the cable 30 afterinstallation, for example, by adhesives.

The shock absorbing device of FIGS. 1 to 3 is shown in functioning modesin FIGS. 4a and 4 b. FIG. 4a shows the device in a relaxed state. Thisis a state in which the cable to which the device is attached is notunder any significant tensile loading. As can be seen from the Figure,the cable is held in a U shape under the action of the resilient member20 and the spacer member 10 is held securely between the base 34 of theU shape and the resilient member 20. Beyond the U shape, the cable 30 isable to follow any desired shape appropriate to the use of the applianceto which the cable 30 is attached.

When the cable 30 is placed under tension, the device adopts theposition shown in FIG. 4b. As the cable 30 is tensioned, so the arms 32of the U shape are moved away from one another as shown. The portions ofthe cable 30 which the resilient member 20 contacts are thereby movedaway from one another as well and the resilient member 20 is forced toextend in a resilient manner. Because the cable 30 is initially wrappedaround the spacer member 10, this tensioning of the cable causes some“unwrapping” from the spacer member 10. Because the spacer member 10 isheld between the base 34 of the U shape and the band 20, the resilientmember 20 begins to wrap itself around the spacer member 10. The spacermember 10 holds the resilient member 10 at a fixed distance from thebase 34 of the U shape. This forces the resilient member 20 to follow anarcuate path between the two points at which the resilient member 20contacts the cable 30. This non-linear relationship between the distancemoved by the points of contact between the cable 30 and the band 20 andthe resilient force created in the band 20 means that the effect is thesame as that of a shock absorber having a rising spring rate.Essentially, this means that, if the contact points between the cable 30and the band 20 are moved apart by a fixed distance, the force requiredto achieve this will increase with the initial distance between thepoints of contact. The advantage of this is that the force required tocompletely straighten the cable 30 will be very high and the risk ofallowing a jerking movement to be applied to the cable will be greatlydiminished. All jerking movements applied, inadvertently or otherwise,to the cable will be damped by the shock absorbing device. The life of acable incorporating this type of device will therefore be less prone tofailure as a result of jerking movements applied during use.

The rising spring rate effect mentioned above has been tested and provento exist in the device described above. In a laboratory experiment, afirst band having the dimensions given above was loaded axially in orderto extend or stretch the band by predetermined amounts. The loadrequired to achieve the extension was then measured. Similarly, a cableincorporating a shock absorbing device as described above was placedunder load and made to extend under the loading by predeterminedamounts. The load required to effect the required extension or stretchwas again measured.

The graph shown in FIG. 5 illustrates the additional loading required toincrease the displacement of each test device by an increment of 2 mmfrom zero displacement to 30 mm displacement. The light columns show theadditional loading required to displace the rubber band whilst the darkcolumns show the additional loading required to displace the shockabsorbing device described above. It is clear from the resultsillustrated in the graph that, the more the shock absorbing device isloaded, the greater the force required to displace the device by apredetermined amount. The presence of a rising spring rate effect isquite clear.

The invention is not limited to the precise details of the embodimentdescribed above. It will be appreciated, for example, that the spacermember need not be absolutely rigid and that a similar effect can beachieved if the spacer member were made from, for example, a denserubber or synthetic rubber. FIGS. 6 to 8 illustrate embodiments in whichthe spacer member is made resiliently deformable. In FIG. 6, the spacermember 100 is annular when the cable is not under tension (see FIG. 6a)but can be deformed when the cable 130 is under tension as shown in FIG.6b. The spacer member 100 a could also be made from a highly resilientmaterial such as a foamed rubber as shown in FIG. 7. Such a spacermember 100 a would then deform from a circular shape into a distortedoval shape when the cable 130 a was put under tension. A furtheralternative is illustrated in FIG. 8 which shows a mildly resilientspacer member 100 b having a plurality of cut-out portions 150 withinthe circular periphery of the spacer member 100 b. These cut-outportions 150 contain plugs 152 of readily-deformable material whichallow the spacer member 100 b to deform. The cut-out portions 150 can belocated at any suitable place within the confines of the spacer member100 b.

Manufacturing the spacer member and resilient member from a mouldablematerial such as rubber or a synthetic rubber would allow the entiredevice to be manufactured as a single piece if desired, ie with theresilient band formed integrally with the spacer member. One advantageof manufacturing the device as a single piece is that the two parts ofthe device shown in FIGS. 1 to 4 can never then become separated so thatthe device becomes useless. Loss or misplacement of the resilient membermight encourage a user to substitute a band of different dimensions andresilience which could easily be inferior in performance or could onoccasion be dangerous. An embodiment of a single piece device is shownand illustrated in FIG. 9. FIG. 9a shows a spacer member 200 mouldedfrom a rubber or synthetic rubber and having a groove 216 around theperiphery thereof as has been previously described. The resilient member220, in the form of a rubber band, is moulded integrally therewith andis joined to the spacer member 200 on the side of the spacer member 200opposite the groove 216. The spacer member 200 also has an outwardlyprojecting stopper 218 for retaining the band 220 on the correct side ofthe spacer member 200. In use, the cable is formed into a U shape andthe base of the U shape is passed through the band 220. The spacermember 200 is then turned so that it lies in the same plane as the cableand placed within the U shape between the base thereof and the band 220.The cable is then pulled outwardly to press the band 220 against thespacer member 200 and thereby hold it in position. The stopper 218prevents the free side of the band 220 from slipping past the spacermember 200. Alternative arrangements having equivalent parts areillustrated in FIGS. 9b, 9 c and 9 d.

It is equally possible to form the device from a spacer member and aresilient member which have been manufactured separately but which arefixed together during manufacture so as to be inseparable thereafter.This also alleviates the problem of the two parts of the devicedescribed in detail above becoming separated and one or the other beingmisplaced. In each of the embodiments shown in FIGS. 9a to 9 d, thespacer member and band can be manufactured separately and fixedly joinedtogether by, for example adhesion.

There are also ways of holding the resilient member against the spacermember other than that shown in the drawings so far described. FIG. 10shows an arrangement in which the spacer member 300 has a slot 310arranged in the side thereof opposite the groove which receives thecable 330. When the device is placed in position, the portions of theband 320 which lie between the cable portions are received into the slot310 so that further movement of the band 320 towards the base of the Ushape of the cable 330 is prevented. FIG. 11 shows a further alternativearrangement in which the ends 425 of the band 420 are fixedly attachedto the spacer member 400 and the centre portion of the band 420 isreceived in a radial slot 410 formed in the spacer member 400. Thespacer member 400 maintains the band 420 at a fixed distance from thecable 430. FIG. 12 shows an embodiment in which the band 520 itselfcarries inwardly projecting portions 525 which are received in recesses510 in the spacer member 500 in order to maintain the band 520 at afixed distance from the cable 530. These embodiments are all equallyviable and are intended to fall within the scope of the invention.

The skilled reader will also appreciate that the spacer member is notrequired to be circular or annular in shape. The requirement is that thespacer member spaces the base of the U shape away from the resilientmember in order to maintain the base and the resilient member at a fixedminimum distance. This ensures that the “unwrapping” of the cable fromthe spacer member causes the resilient member to wrap, at least partly,around the spacer member. It is this action which creates the risingspring rate effect and ensures that the damping of jerking movementsapplied to the cable is effective. This can be achieved merely by theprovision of bracing arms or stops on a small spacer member, the bracingarms serving to hold the cable away from the resilient member withoutforcing the cable to follow a predetermined circular path.

It is also considered advantageous if the cable is guided into a linearshape outside the confines of the devices illustrated above. FIG. 13shows an embodiment which includes bracing arms 610 located on thespacer member 600. These bracing arms 610 guide the cable 630 back intoa linear shape outside the confines of the device.

Another advantageous feature is the provision of a cable protectingsheath or cover which will enclose the cable as it passes around thespacer member. The sheath or cover can be manufactured with the devicesdescribed above, or else it can be manufactured separately and fitted tothe device after installation. The sheath or cover can take the form ofa plastics moulded cover which can be snap-fitted to the spacer memberso as to cover the part of the cable which, in use, is wrapped aroundthe spacer member. This would protect the user of an appliance poweredby means of the cable in the event of a failure of the cable at thepoint at which the device is fitted.

The resilient member is here described as a simple elastomeric band. Itwill be appreciated that the same effects can be achieved using otherresilient members such as tension springs and solid elastomeric members.The simple band is preferred in the embodiment illustrated for reasonsof ease of application, but other types of resilient member are equallysuitable.

What is claimed is:
 1. A shock absorbing device for an electric cablecomprising a resilient member attachable to two spaced-apart portions ofthe cable so as to bias the said portions towards one another and toimpart an arcuate shape to the cable between the said portions, thedevice further comprising a spacer member for location between the cableand the resilient member.
 2. A shock absorbing device as claimed inclaim 1, wherein retaining means for retaining the resilient member incontact with the spacer member are provided on the spacer member.
 3. Ashock absorbing device as claimed in claim 2, wherein the retainingmeans comprise at least one hook shaped member.
 4. A shock absorbingdevice as claimed in claim 3, wherein the or each hook shaped memberdelimits a groove in which the resilient member is, in use, retained. 5.A shock absorbing device as claimed in claim 4, wherein the width of theor each groove is less than the thickness of the resilient member whenin a relaxed state.
 6. A shock absorbing device as claimed in claim 1,wherein, in use, the cable forms a U shape between the two spaced-apartportions, the arms of the U shape being connected together by theresilient member and the spacer member being located between theresilient member and the base of the U shape.
 7. A shock absorbingdevice as claimed in claim 6, wherein the spacer member has at least onebracing portion for urging the cable, outside the U shape, into a linearshape.
 8. A shock absorbing device as claimed in claim 7, wherein acable protecting cover or sheath is provided to cover the cable, atleast in part, lying in use between the two spaced-apart portionsthereof.
 9. A shock absorbing device as claimed in claim 6, wherein, inuse, the application of a tensile force to the cable results in theresilient member becoming wrapped at least partly around the spacermember.
 10. A shock absorbing device as claimed in claim 1, wherein thespacer member has two opposing faces, the planes of the opposing facesbeing inclined to one another.
 11. A shock absorbing device as claimedin claim 10, wherein the retaining means are provided on the spacermember in the area in which the planes of the opposing faces arefurthest apart.
 12. A shock absorbing device as claimed claim 1, whereinthe resilient member comprises a resilient band.
 13. A shock absorbingdevice as claimed in claim 12, wherein the resilient member is made fromrubber or a rubberised plastics material.
 14. A shock absorbing deviceas claimed in claim 1, wherein, in use, the resilient member actsdirectly on the cable.
 15. A shock absorbing device as claimed in claim14, wherein, in use, the resilient member is retained on the cablesolely by frictional forces.
 16. A shock absorbing device as claimed inclaim 1, wherein the member is formed separately from the spacer member.17. A shock absorbing device as claimed in claim 16, wherein theresilient member and the spacer member are fixedly connected together.18. A cable comprising a shock absorbing device as claimed in claim 1.19. A vacuum cleaner comprising a cable as claimed in claim
 18. 20. Ashock absorbing device as claimed in claim 1, wherein, in use, the cableis wrapped around at least part of the spacer member.
 21. A shockabsorbing device as claimed in claim 1, wherein the spacer member iscircular.
 22. A shock absorbing device as claimed in claim 1, whereinthe spacer member is annular.
 23. A shock absorbing device as claimed inclaim 1, wherein the resilient member and the spacer member are formedintegrally.
 24. A cable comprising a plurality of shock absorbingdevices as claimed in claim
 1. 25. A shock absorbing device for anelectrical cable, comprising a resilient member attachable to twospaced-apart portions of the cable so as to bias the spaced-apartportions toward one another and to impart an arcuate shape to the cablebetween the spaced-apart portions, the device further comprising aspacer member for location between the cable and the resilient member,wherein the spacer member has a groove located around the peripherythereof for receiving the cable.